Multiple Screen Detection Systems

ABSTRACT

The present invention is a detection system and method for using the detection system in radiant energy imaging systems. In particular, the present invention is an improved detection system employing multiple screens for greater detection efficiency. And more particularly, the present invention is a detection system for detecting electromagnetic radiation having an enclosure having four adjacent walls, connected to each other at an angle and forming a rectangle and interior portion of the enclosure, a front side area and a back side area formed from the four adjacent walls and located at each end of the enclosure, at least two screens, that further include an active area for receiving and converting electromagnetic radiation into light, and a photodetector, positioned in the interior portion of the enclosure, having an active area responsive to the light.

CROSS-REFERENCE

The present application relies upon, for priority, U.S. ProvisionalApplication No. 60/984,640, filed on Nov. 1, 2007.

FIELD OF THE INVENTION

The present invention relates generally to the field of radiant energyimaging systems. In particular, the present invention relates todetection systems and methods of using the detection systems in radiantenergy imaging systems. And more particularly, the present inventionrelates to an improved detection system employing multiple screens forgreater detection efficiency.

BACKGROUND OF THE INVENTION

Security systems are presently limited in their ability to detectcontraband, weapons, explosives, and other dangerous objects concealedunder clothing. Metal detectors and chemical sniffers are commonly usedfor the detection of large metal objects and some varieties ofexplosives, however, a wide range of dangerous objects exist that cannotbe detected with these devices. Plastic and ceramic weapons developed bymodern technology increase the types of non-metallic objects thatsecurity personnel are required to detect; the alternative of manualsearching of subjects is slow, inconvenient, and is not well-toleratedby the general public, especially as a standard procedure in, forexample, airports.

Further, radiation exposure is an important consideration in X-rayconcealed object detection systems. This issue is addressed in theAmerican National Standard “Radiation Safety for Personnel SecurityScreening Systems Using X-rays” (ANSI/HPS N43.17-2002). This standardpermits a radiation exposure of 0.1 microsievert (10 microrem) per scanfor security inspection of the general public. It is based on therecommendations of the United States National Council on RadiationProtection (NCRP) in NCRP Report No. 91, “Recommendations on Limits forExposure to Ionizing Radiation”, 1987. In this report, the NCRP statesthat the health risk of a radiation exposure of less than 10microsieverts (1000 microrem) per year is negligible, and efforts arenot warranted at reducing the level further. Persons employed in highsecurity or secured facilities, or those who frequently travel byairlines, may be subjected to many security examinations per year. Thestandard criterion thus assures that an individual inspected less thanabout 100 times per year will not receive a non-negligible radiationdose.

Conventional systems and methods for detecting objects concealed onpersons have limitations in their design and method which prohibit themfrom achieving both low dose and high image quality which areprerequisites of commercial acceptance. Specifically, conventional priorart systems for people screening are designed such that they detectradiant energy that has been transmitted through the body, scatteredfrom the body, and/or emitted from the body. In addition, inconventional people screening systems, images are produced by bodycharacteristics and any object concealed under the subject's clothing.The system operator then inspects each image for evidence of concealedobjects.

An example of such a system is described in U.S. Pat. No. RE 28544,assigned to American Science and Engineering, describes a “radiantenergy imaging apparatus comprising: a source of a pencil beam of X-rayradiant energy; radiant energy detecting means defining a curve in fixedrelationship to said source; means for scanning with said pencil beamsaid radiant energy detecting means along said curve to provide an imagesignal representative of the radiant energy response of the medium in aregion traversed by said pencil beam along a path to said detectingmeans; means for relatively displacing said region and an assemblycomprising said source and said detecting means to establish relativetranslating motion in a direction transverse to a line joining saidsource and said detecting means to produce a sequence of image signalsrepresentative of the radiant energy response of said region in twodimensions; and means responsive to said image signals for producing animage representative of said response.”

U.S. Pat. No. 5,181,234, assigned to the assignee of the presentinvention, and herein incorporated by reference, discloses “X-rayimaging apparatus for detecting a low atomic number object carried by oron a human body positioned at a distance from said apparatus comprising:x-ray source for producing a pencil beam of X-rays directed toward saidhuman body; scanning means for moving the region of intersection of saidpencil beam and said human body over the surface of said human body in ascanning cycle, said scanning cycle being sufficiently short to exposesaid human body to a low radiation dose; a detector assembly providing asignal representative of the intensity of the X-rays scattered from saidhuman body as a result of being scanned by said scanning means, saiddetector assembly being disposed on a same side of said human body assaid X-ray source and having an active area with dimensions sufficientto receive a substantial portion of said scattered X-rays to provide acoefficient of variation of less than 10 percent in said signal; anddisplay means to presenting characteristics of the detector signal to anoperator; wherein said scattered X-rays are distributed across saiddetector to create an edge effect which enhances edges of said lowatomic number object to enable detection.”

In addition, prior art baggage inspection systems include detectionmeans for both transmitted and backscattered X-rays to independentlyproduce signals from the same incident beam. The separate signals maythen be used to enhance each other to increase the system's accuracy inrecognizing low Z materials. Clearly, with the incident beam being ofsufficient energy to provide both transmitted and backscattered signals,the X-ray energy must be relatively high, making such systemsundesirable for personnel inspection. An example of such a system isU.S. Pat. No. 4,799,247, assigned to Annis et al., which discloses “aprojection imaging system for inspecting objects for highlighting low Zmaterials comprising: a source of penetrating radiation, means forforming radiation emitted by said source into a beam of predeterminedcross-section and for repeatedly sweeping said beam across a line inspace, means for moving said object to be imaged relative to said sourcein a direction perpendicular to said line in space, first radiant energydetector means located to be responsive to radiant energy penetratingsaid object and emerging from said object, substantially unchanged indirection, for producing first electrical signals, second radiant energydetector means located further from said source than said object andresponsive to radiant energy scattered by said object for producingsecond electrical signals, third radiant energy detector means locatedcloser to said source than said object and responsive to radiant energyscattered by said object for producing third electrical signals, displaymeans responsive to at least a pair of said electrical signals forseparately, independently and simultaneously displaying said pair ofelectrical signals as a function of time”.

As mentioned above, conventional systems and methods have limitationsthat prohibit them from achieving both low dose and high image qualitywhich are prerequisites of commercial acceptance. In addition, inconventional people screening systems, images are produced by bodycharacteristics and any object concealed under the subject's clothing.

The prior art systems are disadvantageous, however, because they do notadequately detect plastics, ceramics, explosives, illicit drugs, andother non-metallic objects. One reason in particular is that thesematerials share the property of a relatively low atomic number (low Z).Low Z materials present a special problem in personnel inspectionbecause of the difficulty in distinguishing the low Z object from thebackground of the subject's body which also has low Z. An inspectionsystem which operates at a low level of radiation exposure is limited inits precision by the small number of X-rays that can be directed againsta person being searched. X-ray absorption and scattering further reducesthe number of X-rays available to form an image of the person and anyconcealed objects. In prior art systems, this low number of detectedX-rays has resulted in unacceptably poor image quality.

Therefore, what is needed is a method and apparatus that increases theefficiency of a detector to detect electromagnetic radiation and improvethe quality of the resultant image generated, thus reducing the overallamount of radiation required.

What is also needed is a method for using an improved radiant energyimaging system with enhanced detection capabilities.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus andmethod for increasing the efficiency of a detector to detectelectromagnetic radiation and improve the quality of the resultant imagegenerated, thus reducing the overall amount of radiation required.

It is another object of the present invention to provide a detectorconfiguration that maximizes the efficiency of the detector material. Itis yet another object of the present invention to absorb more X-rayphotons and thus, improve detection capability.

In one embodiment, the present invention is a detection system fordetecting electromagnetic radiation comprising: an enclosure having fouradjacent walls, connected to each other at an angle and forming arectangle and interior portion of the enclosure; a front side area and aback side area formed from the four adjacent walls and located at eachend of the enclosure; at least two screens, wherein each screen furthercomprises an active area for receiving and converting electromagneticradiation into light; and a photodetector, positioned in the interiorportion of the enclosure, having an active area responsive to the light.

In another embodiment, the present invention is a detection system fordetecting electromagnetic radiation comprising: an enclosure having fouradjacent walls, connected to each other at an angle and forming arectangle and interior portion of the enclosure; a front side area and aback side area formed from the four adjacent walls and located at eachend of the enclosure; a screen located in the front side area, furthercomprising an active area for receiving and converting electromagneticradiation into light; at least one screen located in the interiorportion of the enclosure; and a photodetector, positioned in theinterior of the enclosure, having an active area responsive to thelight.

In one embodiment, the front side area is formed from at least one ofthe plurality of screens. In another embodiment, the active area on eachof the plurality of screens comprises a scintillator material, where thescintillator material is calcium tungstate. In one embodiment, thephotodetector is a photomultiplier tube.

In one embodiment, the detection system enclosure is capable ofreceiving, but not leaking electromagnetic radiation. In anotherembodiment, the interior surface of the adjacent enclosing walls islight reflective.

In one embodiment, the active area of at least one of the plurality ofscreens is larger than the active area of the photodetector and theareal density is 80 mg/cm².

In one embodiment, the surface geometry of at least one of the pluralityof screens is straight or smooth. In another embodiment, the surfacegeometry of at least one of the plurality of screens is irregular. Inyet another embodiment, the surface geometry of at least one of theplurality of screens is contoured. In still another embodiment, thesurface geometry of at least one of the plurality of screens iscorrugated.

In another embodiment, the present invention is a radiant energy imagingsystem comprising: a radiation source; a detection system, comprising i)an enclosure having four adjacent walls, connected to each other at anangle and forming a rectangle and interior portion of the enclosure; ii)a front side area and a back side area formed from the four adjacentwalls and located at each end of the enclosure; iii) a plurality ofscreens, wherein each screen further comprises an active area forreceiving and converting electromagnetic radiation into light; and iv) aphotodetector, positioned in the interior of the enclosure, having anactive area responsive to the light; an image processor for receivingsignals from the photodetector and generating an image; and a displayfor displaying the image generated.

In one embodiment, the radiant energy imaging system is a peoplescreening system. In another embodiment, the radiant energy imagingsystem is a baggage screening system.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated, as they become better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, wherein:

FIG. 1 is a front view illustration of a conventional detectorenclosure, having one screen;

FIGS. 2 a and 2 b illustrate the incidence of electromagnetic radiationon a first screen of a conventional detector enclosure;

FIG. 3 illustrates one embodiment of the detector enclosure of thepresent invention, having a plurality of screens, showing the incidenceof electromagnetic radiation on the plurality of screens;

FIG. 4 illustrates another embodiment of the detector enclosure of thepresent invention, having a plurality of screens, showing the incidenceof electromagnetic radiation on the plurality of screens;

FIG. 5 illustrates one embodiment of a backscatter inspection system inwhich any of the detector enclosures of the present invention can beimplemented; and

FIG. 6 illustrates one embodiment of a traditional transmission X-rayscreening system in which any of the detector enclosures of the presentinvention can be implemented.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed towards several embodiments of anelectromagnetic radiation detector in which a plurality of screens isemployed. The present invention is directed towards a detection systemenclosure having at least one screen. Electromagnetic radiation isabsorbed by the screen which emits light photons that are detected by aphotomultiplier tube located within the enclosure. In one embodiment,the detection system of the present invention has one screen located atthe front of the enclosure and at least one screen located in theinterior of the enclosure. In one embodiment, the at least one screencomprises an active area for receiving and converting electromagneticradiation into light (photons). In one embodiment, the active area ofthe at least one screen comprises a scintillator material. In oneembodiment, the scintillator material is calcium tungstate.

In one embodiment, the at least one screen has a thickness (arealdensity) of 80 mg/cm². In one embodiment, the surface geometry of the atleast one screen is straight or smooth. In one embodiment, the surfacegeometry of the at least one screen is irregular. In another embodiment,the surface geometry of the at least one screen is contoured. In anotherembodiment, the surface geometry of the at least one screen iscorrugated; a corrugated surface geometry provides a greater surfacearea for receiving and converting electromagnetic radiation into light,by allowing for an increase in the electromagnetic radiation path lengthwithout increasing the light output path length, for maximum detectionefficiency. It should be understood by those of ordinary skill in theart that any surface geometry may be used for the screen to increase theamount of electromagnetic radiation absorbed.

The present invention is also directed towards the use of at least onescreen in the interior of the enclosure, thus increasing the amount ofelectromagnetic radiation reaching the detector, and subsequently, theamount of photons reaching the photomultiplier. In one embodiment, theat least one screen located in the interior of the enclosure hasidentical specifications to the screen located in the front of theenclosure. In one embodiment, the at least one screen positioned in theinterior of the enclosure is different from the screen located in thefront of the enclosure, in terms of at least one of chemicalcomposition, surface geometry, thickness and energy response. The use ofa screen at the front of the enclosure and the at least one screen inthe interior of the enclosure increases the amount of electromagneticradiation absorbed and therefore, the number of photons generated,further improving detection capability, and thus image quality.

Thus, the present invention is directed towards a detector configurationthat maximizes the efficiency of the detector material. Detectionefficiency is a measure of the efficiency of the detector screen, or,the probability that electromagnetic radiation will be absorbed by thescreen to produce light photons detectable by the photomultiplier tube.X-ray detectors need to interact with incident x-ray photons to recordtheir presence; x-rays that pass through the detector withoutinteraction are wasted. Detection efficiency is mainly determined by theinteraction probability of the photons with the detector material andthe thickness of the material. The following equation can be used tocalculate the efficiency of a detector:

I=I ₀ *e ^(−μx)

where I₀ is the number of photons of a certain energy incident orentering the slab of material; x is the thickness of the slab, I is thenumber of photons that have passed through a layer of thickness x, and μis the linear attenuation coefficient of the material for photons ofthis particular energy. The photons that do not get through haveinteracted within the slab of material and are either absorbed orscattered. The number of photons absorbed by a certain thickness is thedifference I0−I. However, instead of calculating for different I's, theratio of (I0−I)/I is calculated and it is called the “PercentAbsorption.” Conventional screens typically achieve far less than 100%efficiency. The present invention is directed toward absorbing more ofthe otherwise wasted X-ray photons and thereby improving the detectioncapability.

In another embodiment, the present invention is also directed towards adetection system enclosure that further comprises a photo-multipliertube, positioned in the interior of the enclosure, having an active arearesponsive to the light. In another embodiment, the active area of theat least one screen is larger than the active area of thephoto-multiplier tube so that the amount of electromagnetic radiationabsorbed is maximized.

The present invention is directed towards multiple embodiments. Languageused in this specification should not be interpreted as a generaldisavowal of any one specific embodiment or used to limit the claimsbeyond the meaning of the terms used therein. Reference will now be madein detail to specific embodiments of the invention. While the inventionwill be described in conjunction with specific embodiments, it is notintended to limit the invention to one embodiment.

FIG. 1 is a front view illustration of a conventional detectorenclosure, having one screen. Detector 100 comprises an enclosure havingfour adjacent walls, 102 a, 102 b, 102 c, and 102 d, connected to eachother at an angle. The four adjacent walls 102 a, 102 b, 102 c, and 102d form a rectangular shape. Adjacent walls 102 a, 102 b, 102 c, and 102d further form a front side area 106 and a back side area 104 at theends of the enclosure. The enclosure formed from adjacent walls 102 a,102 b, 102 c, 102 d, front side area 106 and back side area 104 iscapable of receiving, but not leaking electromagnetic radiation, therebyblocking the exit of incoming radiation from a radiation source. Theability of the enclosure to receive, and not leak, radiation, isfacilitated by the light reflective interiors of the enclosing walls.Typically, the interiors of walls 102 a, 102 b, 102 c, and 102 d arepainted white so that they are highly light reflective.

The front side area 106 of detector enclosure 100 is used for receivingradiation and thus faces the object under inspection when in use in anexemplary scanning system. Front side area 106 further comprises ascreen 107. Detector enclosure 100 further comprises a photo-detector108, placed in the interior of the enclosure proximate to back side area104. The photo-detector 108 is a photomultiplier tube. Photomultipliertubes are well-known to those of ordinary skill in the art and will notbe discussed herein.

FIGS. 2 a and 2 b illustrate the incidence of electromagnetic radiationon a first screen of a conventional detector enclosure. In operation,the screening system directs electromagnetic radiation from a sourcetoward a subject or object under inspection such that the X-rays areincident upon the subject or object. The X-rays are then, depending uponthe intensity of the X-ray and the type of inspection system beingemployed, scattered from or transmitted through the subject or objectunder inspection. The radiation source and the nature of the X-ray beamare described in detail with respect to FIGS. 5 and 6 below and will notbe discussed further.

Now referring to FIG. 2 a scattered or transmitted X-rays 210 reach thedetector enclosure 200 and first impinge upon screen 207. Screen 207absorbs at least a portion of the scattered or transmitted X-rays 210and converts the X-rays into light photons 206 in the interior ofdetector enclosure 200. As shown in FIG. 2 b, however, some of theX-rays are not absorbed and thus pass through screen 207. In addition,in a conventional detector enclosure with only one front screen, atleast a portion of photons 206 reflect off of the highly reflectiveinterior walls of the enclosure and are subsequently detected byphotomultiplier tube 208.

Referring to FIG. 3, the present invention is a detector enclosurecomprising at least one additional screen (not shown in FIGS. 2 a and 2b) in the interior of the enclosure. The at least one additional screenfurther increases the exposure rate of the scattered or transmittedX-rays 210. The net effect of the at least one additional screen is toincrease the photo-detection efficiency of photomultiplier tube 208 byabsorbing more electromagnetic radiation, subsequently converting thatradiation to light, and thus, providing the photomultiplier tube with astronger signal to detect.

FIG. 3 illustrates one embodiment of the detector of the presentinvention, having a plurality of screens. Detector enclosure 300 issimilar to the enclosure described with respect to FIG. 1, in that itcomprises four adjacent side walls, the proximal sides of which form afront side area 306 and distal sides of which form a back side area 304.One of ordinary skill in the art should appreciate that the detectorenclosure of FIG. 1 can be modified to create the embodiment shown inFIG. 3.

Referring now to FIG. 3, first screen 307 a is located on the front sidearea 306 of detector enclosure 300. In one embodiment, second and thirdscreens 307 b and 307 c are positioned inside the detector enclosure300. The X-rays scattered from or transmitted through the subject orobject under inspection 310 first impinge upon first screen 307 a ofdetector enclosure 300. Some of the scattered or transmitted X-rays,however, are not absorbed by first screen 307 a and thus pass throughfirst screen 307 a.

To increase detection efficiency, in one embodiment, detector enclosure300 further comprises second and third screens, 307 b and 307 c,respectively in the interior of the enclosure. Second and third screens,307 b and 307 c, respectively, further increase the exposure rate andthus, absorption of the scattered or transmitted X-rays 310. The overalleffect of the first, second, and third screens is an increase in thephoto-detection efficiency of photomultiplier tube 308 by absorbing moreelectromagnetic radiation, subsequently converting that radiation tolight, and thus, providing the photomultiplier tube with a strongersignal to detect.

In one embodiment, first screen 307 a comprises an active area forreceiving and converting electromagnetic radiation into light (photons).In one embodiment, first screen 307 a is a fluorescent chemical screen.In one embodiment, scintillators in the fluorescent chemical screen 307a detect a large fraction of the incident radiation, produce significantlight output to the photomultiplier tube, and exhibit a temporal decaytime which is short compared to the pixel to pixel scanning rate of theradiation beam.

In one embodiment, the fluorescent chemical screen includes calciumtungstate. Generally, a calcium tungstate screen has a relatively shortdecay time of 10 microseconds that allows rapid scanning of theradiation beam with minimal image degradation. The calcium tungstatescreen is capable of detecting approximately 70% of the backscattered ortransmitted radiation, and thus, produces approximately 250 usable lightphotons per 30 KeV X-ray.

Additionally, the use of a thicker screen enables the detection of moreof the radiation incident upon the detector at the expense of lowerlight output. In one embodiment, the areal density of the screen is 80milligrams per square centimeter.

In one embodiment, the at least one screen located in the interior ofthe enclosure has identical specifications to the screen located in thefront of the enclosure. Thus, in one embodiment, second and thirdscreens 307 b and 307 c, respectively, are identical to first screen 307a. In one embodiment, the at least one screen positioned in the interiorof the enclosure is different from the screen located in the front ofthe enclosure, in terms of at least one of chemical composition, surfacegeometry, thickness and energy response. Thus, in one embodiment, secondand third screens 307 b and 307 c, respectively, are different fromfirst screen 307 a.

Although exemplary screens have been described above, it should be notedthat the characteristics of the screen can vary widely in terms ofchemical composition, surface geometry, thickness and energy response,and that any type of screen may be used in the present invention, aswould be evident to those of ordinary skill in the art.

FIG. 4 illustrates another embodiment of the detector enclosure of thepresent invention, having a plurality of screens. In one embodiment, thesurface geometry of the at least one screen is straight or smooth. Inone embodiment, the surface geometry of the at least one screen isirregular. In another embodiment, the surface geometry of the at leastone screen is contoured. In another embodiment, the surface geometry ofthe at least one screen is corrugated. A corrugated surface geometryprovides a greater surface area for receiving and convertingelectromagnetic radiation into light, by allowing for an increase in theelectromagnetic radiation path length without increasing the lightoutput path length, for maximum detection efficiency. It should beunderstood by those of ordinary skill in the art that any surface typemay be used for the screen to increase the amount of electromagneticradiation absorbed.

In one embodiment, screen 407 located on front side area 404 of detectorenclosure 400 is corrugated. The corrugated surface of screen 404provides a greater surface area for absorbing scattered or transmittedelectromagnetic radiation 410, incident upon the detector enclosure 400.It should be noted that because light generated in spaces 411, definedby screens 407 and 408, cannot escape easily, the detection efficiency,or effective detection area is reduced.

FIG. 5 illustrates one embodiment of a scanning system in which any ofthe detector enclosures of the present invention can be implemented. Inone embodiment, the detector enclosure of the present invention isemployed in a backscatter X-ray scanning system, such as but not limitedto a people screening system. In one embodiment, inspection system 500comprises radiation source 508 and at least one detector enclosure 502.As described in detail above, the at least one detector enclosure 502may comprise any number of arrangements including, but, not limited toat least one detector screen. In addition, at least one detectorenclosure 502, in another embodiment, may comprise any number ofarrangements including, but, not limited to a plurality of detectorscreens. While various arrangements of detectors will not be repeatedherein, it should be understood by those of ordinary skill in the artthat any number of detector arrangements can be employed, as describedabove and the exemplary embodiment is not intended to limit the presentinvention.

Referring back to FIG. 5, X-ray source 508 is used to generateradiation. In one embodiment, X-ray source 508 is employed to generate anarrow pencil beam 506 of X-rays directed towards an object or subjectunder examination 504. In one embodiment, pencil beam is formed with theintegration of an x-ray tube, a mechanical chopper wheel, and a slit.

In one embodiment, x-ray source 508 operates with an empirically andtheoretically determined optimum X-ray tube potential of 50 KeV and 5milliamps, resulting in X-rays of approximately 30 KeV. The vertical andhorizontal dimension of the X-ray beam is approximately six millimeters(6 mm) where it strikes subject 504. Subject 504 is a body that is beingsubjected to X-ray imaging. In one embodiment, subject 504 is a human.In another embodiment, subject 504 is an object. Initially, X-ray beam506 strikes only the body of subject 504. Many of the X-rays penetrate afew centimeters into the body, interact by Compton scattering, and exitthe body through the same surface that they entered. X-ray sensitivedetector enclosures 502 are placed symmetrically around incident X-raypencil beam to detect backscattered X-rays 510 and provide an electronicsignal characteristic of the X-ray reflectance. It should be understoodto those of ordinary skill in the art that any number of ionizingradiation sources may be used, including but not limited to gammaradiation, electromagnetic radiation, and ultraviolet radiation.

Detectors 502 are positioned for uniform X-ray detection on all sides ofX-ray beam 506. In one embodiment, arrays of detectors 502 are placedaround source 508 for uniform detection of backscattered rays 510.Detectors 502 include an enclosure capable of enclosing or “trapping”scattered rays 510. A photo-detector generates electronic signals inresponse to detected rays that are initially converted into light.Details about the structure and operation of several embodiments of adetector 502 are discussed in detail with respect to FIGS. 1-4 and willnot be repeated herein.

In one embodiment, each detector 502 produces electronic signals whichare directed to a processor. The processor analyzes the received signalsand generates an image on a display means 512. The intensity at eachpoint in the displayed image corresponds to the relative intensity ofthe detected scattered X-rays. In one embodiment, X-ray source 508communicates synchronization signals to the processor. The processoranalyzes the detected signals and compares them to the synchronizationsignals to determine the display image.

In one embodiment, display means 512 is a monitor and is employed todisplay graphical images signaled by the processor. Display means 512can be any display or monitor as commonly known in the art, including acathode ray tube monitor or an LCD monitor. In one embodiment, thedigitized scatter image displayed by display means 512 preferablyconsists of 480 rows by 160 columns with 8 bits per pixel.

Referring back to FIG. 5, detectors 502 are separated by an openingthrough which x-ray beam 506 passes before striking subject 504. In oneembodiment, detectors 502 can move in a vertical direction while X-raybeam 506 moves in a horizontal direction by movement of X-ray source 508in the horizontal direction. However, the placement and movement ofdetectors 502 and source 508 is not limited to the description providedherein. In other embodiments, detectors 502 and source 508 can be placedand moved by any method as is commonly known in the art. Theintersection of x-ray beam 506 and subject 504 defines an image pictureelement (pixel) of a specified area.

FIG. 6 illustrates another embodiment of a scanning system in which anyof the detector enclosures of the present invention can be implemented.In another embodiment, the scanning system is a traditional X-rayscanning system, in which X-rays are transmitted through the objectunder inspection. In one embodiment, the traditional transmission X-rayscanning system is a baggage scanning system.

In one embodiment, inspection system 600 comprises radiation source 608and at least one detector enclosure 602. As described in detail above,the at least one detector enclosure 602 may comprise any number ofarrangements including, but, not limited to at least one detectorscreen. In addition, at least one detector enclosure 602, in anotherembodiment, may comprise any number of arrangements including, but, notlimited to a plurality of detector screens. While various arrangementsof detectors will not be repeated herein, it should be understood bythose of ordinary skill in the art that any number of detectorarrangements can be employed, as described above and the exemplaryembodiment is not intended to limit the present invention.

Referring back to FIG. 6, X-ray source 608 is used to generateradiation. In one embodiment, X-ray source 608 is employed to generate anarrow pencil beam 606 of X-rays directed towards an object or subjectunder examination 604. In one embodiment, pencil beam is formed with theintegration of an x-ray tube, a mechanical chopper wheel, and a slit.

Object 604 is an item that is subjected to X-ray imaging. In oneembodiment, object 604 is a piece of luggage or carry-on baggage.Initially, X-ray beam 606 strikes only the object 604. Many of theX-rays are transmitted through the object, interact by Comptonscattering, and exit the object through the opposite surface that theyentered. X-ray sensitive detector enclosures 602 are placedsymmetrically around incident X-ray pencil beam to detect transmittedX-rays 610 and provide an electronic signal characteristic of the X-raytransmission.

It should be understood to those of ordinary skill in the art that anynumber of ionizing radiation sources may be used, including but notlimited to gamma radiation, electromagnetic radiation, and ultravioletradiation.

Detectors 602 are positioned for uniform X-ray detection on all sides ofX-ray beam 606. In one embodiment, arrays of detectors 602 are placedaround object 604 for uniform detection of transmitted rays 610.Detectors 602 include an enclosure capable of enclosing or “trapping”scattered rays 610. A photo-detector generates electronic signals inresponse to detected rays that are initially converted into light.Details about the structure and operation of several embodiments of adetector 602 are discussed in detail with respect to FIGS. 1-4 and willnot be repeated herein.

In one embodiment, each detector 602 produces electronic signals whichare directed to a processor. The processor analyzes the received signalsand generates an image on a display means 612. The intensity at eachpoint in the displayed image corresponds to the relative intensity ofthe detected transmitted X-rays. In one embodiment, X-ray source 608communicates synchronization signals to the processor. The processoranalyzes the detected signals and compares them to the synchronizationsignals to determine the display image. In one embodiment, display means612 is a monitor and is employed to display graphical images signaled bythe processor. Display means 612 can be any display or monitor ascommonly known in the art, including a cathode ray tube monitor or anLCD monitor. In one embodiment, the digitized image displayed by displaymeans 612 preferably consists of 480 rows by 160 columns with 8 bits perpixel.

In one embodiment, detectors 602 can move in a vertical direction whileX-ray beam 606 moves in a horizontal direction by movement of X-raysource 608 in the horizontal direction. However, the placement andmovement of detectors 602 and source 608 is not limited to thedescription provided herein. In other embodiments, detectors 602 andsource 608 can be placed and moved by any method as is commonly known inthe art. The intersection of x-ray beam 606 and object 604 defines animage picture element (pixel) of a specified area.

The above examples are merely illustrative of the many applications ofthe system of present invention. Although only a few embodiments of thepresent invention have been described herein, it should be understoodthat the present invention might be embodied in many other specificforms without departing from the spirit or scope of the invention.Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope of theappended claims.

1. A detection system for detecting electromagnetic radiationcomprising: an enclosure having four adjacent walls, connected to eachother at an angle and forming a rectangle and interior portion of theenclosure; a front side area and a back side area formed from the fouradjacent walls and located at each end of the enclosure; at least twoscreens, wherein each screen further comprises an active area forreceiving and converting electromagnetic radiation into light; and aphotodetector, positioned in the interior portion of the enclosure,having an active area responsive to the light.
 2. The detection systemof claim 1 wherein the enclosure formed from the adjacent walls, frontside area, and back side area receives and does not leak electromagneticradiation.
 3. The detection system of claim 1 wherein the interiorsurface of the adjacent enclosing walls is light reflective.
 4. Thedetection system of claim 1 wherein the front side area is formed fromat least one of the plurality of screens.
 5. The detection system ofclaim 1 wherein the active area on each of the plurality of screenscomprises a scintillator material.
 6. The detection system of claim 4wherein the scintillator material is calcium tungstate.
 7. The detectionsystem of claim 1 wherein the active area of at least one of theplurality of screens is larger than the active area of thephotodetector.
 8. The detection system of claim 1 wherein the arealdensity of at least one of the plurality of screens is 80 mg/cm².
 9. Thedetection system of claim 1 wherein the surface geometry of at least oneof the plurality of screens is straight or smooth.
 10. The detectionsystem of claim 1 wherein the surface geometry of at least one of theplurality of screens is irregular.
 11. The detection system of claim 1wherein the surface geometry of at least one of the plurality of screensis contoured.
 12. The detection system of claim 1 wherein the surfacegeometry of at least one of the plurality of screens is corrugated. 13.The detection system of claim 1 wherein the photodetector is aphotomultiplier tube.
 14. A radiant energy imaging system comprising: aradiation source; a detection system, comprising i) an enclosure havingfour adjacent walls, connected to each other at an angle and forming arectangle and interior portion of the enclosure; ii) a front side areaand a back side area formed from the four adjacent walls and located ateach end of the enclosure; iii) at least two screens, wherein eachscreen further comprises an active area for receiving and convertingelectromagnetic radiation into light; and iv) a photodetector,positioned in the interior of the enclosure, having an active arearesponsive to the light; an image processor for receiving signals fromthe photodetector and generating an image; and a display for displayingthe image generated.
 15. The radiant energy imaging system of claim 14wherein the system is a people screening system.
 16. The radiant energyimaging system of claim 14 wherein the system is a baggage screeningsystem.
 17. A detection system for detecting electromagnetic radiationcomprising: an enclosure having four adjacent walls, connected to eachother at an angle and forming a rectangle and interior portion of theenclosure; a front side area and a back side area formed from the fouradjacent walls and located at each end of the enclosure; a screenlocated in the front side area, further comprising an active area forreceiving and converting electromagnetic radiation into light; at leastone screen located in the interior portion of the enclosure; and aphotodetector, positioned in the interior of the enclosure, having anactive area responsive to the light.